An extrusion press of this type where the counter housing that carries the tool, usually the pressure plate, female die holder and die, and connected to the cylinder beam by tie rods and/or tension beams as well as compression beams is known from DE 102 27 488 [U.S. Pat. No. 7,216,522]. Furthermore, EP 1 526 930 [U.S. Pat. No. 7,421,874] also discloses a metal extrusion press with a compensation tank that is mounted on the piston-cylinder unit for supplying hydraulic fluid under pressure to the press piston and/or piston. The rod supporting the piston disk is provided with an advance and retraction cylinder, and with a hydraulic connection unit attached to the outside of the end wall or rear wall of the equalizing reservoir. The piston disk that is provided on the rod end furthest removed from the piston-cylinder unit housing slides within the equalizing reservoir, the fill space that is closed at the end by the piston disk being connected through connection lines to the cylinder chamber of the piston-cylinder unit that is located in back of the piston, into which space a hydraulic fluid line discharges.
To achieve a high level of efficiency of the presses, nonproductive times must be minimized; in particular, the displacement and lateral cylinders that are provided for the billet support, inside which are provided the billet holder and/or recipient, and the punch crosshead and/or mobile spar must be able to handle idling and retraction at optimum speeds. To this end, large flow volumes must be moved between the cylinders and the oil tank at high flow rates, resulting in turbulent flow and, consequently, foaming due to air trapped in the oil. These disadvantageous operating conditions can only be counteracted by implementing measures of great complexity.
In EP 1 526 930, actuatable check valves are associated with the rod provided in the form of an advance and retraction cylinder in the connection lines that are located in the cylinder base and lead from the fill space of the equalizing reservoir to the cylinder chamber following the piston. What this achieves is that this piston is bathed in oil supplied from the fill space of the equalizing reservoir to effect the piston's advancement to its working position when the check valves are open, there being four of these valves that are formed as two-way integrated valves, also called logic or cartridge valves. The connection lines are closed by the check valves once the piston has reached is working position, the piston being of the same diameter as the equalizing reservoir, and the piston starts the extrusion process, with the result that the slide forces the volume of oil remaining in the equalizing reservoir only into the tank, while the subsequent delivery of hydraulic fluid is now effected only through the hydraulic fluid line, which oil thus does not have to be resupplied, thereby allowing the tank to be at a remote location. This then no longer necessitates having oil lines of large cross-section, such as would be the case without the equalizing reservoir. When the press stroke ends and the return motion of the piston to its starting position is initiated by the associated reversal of the hydraulic unit, the oil flows back into the equalizing reservoir, i.e., the oil is forced back and forth under pressure as the tube/extrusion press operates.
In a frameless metal extrusion press, as disclosed in EP 0 822 017, the handling of large flow volumes is achieved in that two or more press pistons are envisioned that are provided with piston rods of the same diameter traversing their cylinders at both ends, and that the piston rods are sealed on both sides relative to the cylinders, such that cylinder-type partial chambers with areas of equal effectiveness are present on both faces that are connected to each other by a bypass line via a switchable locking valve that can be closed during the working stroke. Special piston drive cylinders are provided for a fast return stroke and high-speed advance on this press. The bypass line that connects the cylinder chambers on both sides of the press piston allows for a quick transfer of the oil from side of the cylinder to the other and with minimal flow resistance, where, however, the bypass lines and the switchable locking valves therein must be quite large.